Stabilizing dispersed colloidal nanosilica exposed to an ultra-high performance concrete environment

Abstract

Uniform dispersion of nanosilica in ultra-high performance concrete is critical in the attempt to enhance its material properties further. Previous studies have shown that well dispersed nanosilica agglomerates when added to concrete. This agglomeration adversely affects the matrix densification, and thus leading to a reduction in mechanical properties. Twelve types of nanosilica and 13 dispersants were investigated in their potential to agglomerate when exposed to a synthetic pore solution that represents the pH and ionic composition in ultra-high performance concrete. More than 1000 dynamic light scattering measurements were performed, analyzed and complemented by zeta-potential measurements, and transmission electron microscopy. It was found that adding polyacrylic acid or hydrochloric acid to nanosilica dispersions before exposing it to the synthetic pore solution could successfully keep the nanosilica stabilized. This dispersion mechanism is needed to avoid agglomeration during the time of mixing cementitious composites and complements recent findings in the literature. Test results of enhanced compressive strength support this hypothesis.